const fp = require('lodash/fp')

class Container {
  static of(value) {
    return new Container(value)
  }

  constructor(value) {
    this._value = value;
  }

  map(fn) {
    return Container.of(fn(this._value));
  }
}

class Maybe {
  static of(x) {
    return new Maybe(x);
  }

  constructor(x) {
    this._value = x;
  }

  isNothing() {
    return this._value === null || this._value === undefined
  }

  map(fn) {
    return this.isNothing() ? this : Maybe.of(fn(this._value));
  }
}

// 1
let maybe = Maybe.of([5,6,1]);
let ex1 = n => maybe.map(arr => fp.map(i => fp.add(i, n), arr));
console.log(ex1(2))

// 2
let xs = Container.of(['do', 'ray', 'me', 'fa', 'so', 'la', 'ti', 'do'])
let ex2 = fn => xs.map(fn)._value;
console.log(ex2(fp.first))

// 3
let safeProp = fp.curry(function(x, o) {
  return Maybe.of(o[x])
})
let user = {id: 2, name: 'Albert'}
let ex3 = () => safeProp('name', user).map(fp.first)._value
console.log(ex3())

// 4
let ex4 = function(n) {
  if(n) {
    return parseInt(n)
  }
}

ex4 = n => Maybe.of(n).map(parseInt)._value
